A Constructed Closure of the Bering Strait to prevent an AMOC tipping

The Atlantic Meridional Overturning Circulation (AMOC) plays a central role in regulating Earth's climate, and is widely considered to be a vulnerable tipping element of the climate system. The Bering Strait Throughflow (BST) can play a key role in the AMOC's stability. Through this narrow passage relatively fresh Antarctic Intermediate Water from the Pacific basin enters the Arctic Ocean and eventually ends up in the deep-water formation zones in the North Atlantic. Moreover, an open Strait enhances the freshwater exchange between the Arctic and North Atlantic. All in all, the Throughflow's net effect is a freshening of the North Atlantic, and hence a weakening of the AMOC. Recent research has indicated that the AMOC is weakening and may reach its tipping point before the end of this century. Since the Bering Strait has limited width and is relatively shallow (approximately 80 km across and on average 50 m deep) constructing a barrier is technically feasible. In this work we show that such a barrier can prevent an AMOC collapse in three levels of the model hierarchy. Firstly, a conceptual model of the World Ocean is extended to include the BST and Arctic amplification, showing that for a low freshwater forcing in the North Atlantic a closure of the Strait prevents an AMOC tipping under climate forcing. Moreover, the conceptual framework allows us to test the sensitivity of the results with respect to BST parametrization and rate of forcing. Next, the conceptual results are reproduced in an Earth system Model of Intermediate Complexity (EMIC). Here we have investigated the AMOC's safe carbon budget for either an open or closed Strait for various freshwater hosing strengths. This reveals an increased carbon budget under a closure given -again- a sufficiently low strength of North Atlantic hosing. Lastly, the closure's effectiveness is tested in a CMIP5 model, namely CESM1. Here an AMOC collapse occurs under RCP8.5 forcing for both a low and high freshwater hosing. In the former the AMOC strength matches observations, while in the latter the overturning-induced freshwater transport through the Atlantic's southern boundary is realistic. In both scenarios a closure of the Bering Strait prevents an AMOC collapse on the condition that this closure occurs sufficiently early. In the strong hosing scenario a closure has to occur at least as early as 2050, while in the low hosing case a closure as late as 2080 is still sufficient. Hence, we have shown throughout the model hierarchy that a closure of the Bering Strait can prevent a collapse of the AMOC, and that it is a potential climate intervention strategy should emissions mitigation fail.